Iron materials have a problem of reacting with molten aluminum to form iron-aluminum alloys, that is, dissolving (being eroded) in molten aluminum.
The problem of erosion also occurs in mechanical components, metal molds, cutting tools, and other tools made of iron materials, including stainless, titanium materials, and superhard materials when they are in contact with molten aluminum.
In order to prevent the erosion, it is considered as a simple and effective means to cover the surface of a substrate made of an iron material or the like to be eroded with a covering member for preventing erosion. In this case, the covering member for preventing erosion should basically have erosion resistance. Since the covering member is usually abruptly brought into contact with molten aluminum, the covering member should also have thermal shock resistance. Furthermore, since the covering material must be visually inspected for degradation, it is necessary for the surface layer to be of a particular color that allows the visual inspection for degradation rather than a common metallic color.
Although various ceramic materials for use in covering members for preventing erosion have a high heat resistance and generally a high erosion resistance, they are brittle and are highly likely to be broken by thermal shock. In the case that the surface of a substrate made of an iron material or the like is coated with a ceramic material, gold-colored titanium nitride (TiN) is advantageous in the visual inspection for degradation but has an insufficient erosion resistance.
Chromium nitride (CrN) having a high erosion resistance [see PTL 1] cannot be visually inspected for degradation because of its metallic color. Titanium silicon nitride (TiSiN) facilitates visual inspection for degradation because of its orange to violet color and is expected to have a higher erosion resistance because of its higher heat resistance than CrN. However, titanium silicon nitride is prone to be broken by thermal shock because of its high hardness.